Seatback



FIG. 1 is a perspective view of a seatback showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a right elevational view thereof;

FIG. 7 is a left elevational view thereof; and,

FIG. 8 is a perspective view of the seatback shown in use with a chair which is shown in broken lines.

The portions shown in broken lines form no part of the claimed design. 

The ornamental design for a seatback, as shown and described. 